Power generating windmills in the past are single-tower windmills having small standalone power generation capacity and low power generation efficiency, and mainly have the following technical problems: first, although much electricity may be generated by increasing the windmill diameter to scale, the weight of the windmill and the generator will be greatly increased, and the service life will be reduced due to the fatigue resulted from the increase of bearing loads, and accordingly, the diameter of an existing maximum wind-driven generator blade will not exceed 200 m; second, by the improvement of the solidity ratio of the windmill blades, a same swept area has a larger wind catch area so that much electricity can be generated, while the solidity ratio of a conventional windmill blade is between 5% and 20%, resulting in the waste of wind resource; and third, the rated wind speed is improved and the most effective (i.e., full-load) power generation time is increased, while the cut-off wind speed of the conventional windmill is generally 25 m/s, and the magnitude of wind energy is in direct proportion to the third power of the wind speed, in other words, only energy at a low wind speed is utilized and considerable wind energy at a high wind speed has to be abandoned. The bi-directional contra-rotating circular-rail bearing Y-shaped compound blade fluid energy collection multi-unit power generating windmill provided by the present invention may overcome these technical problems.